Precise measurement for packaging of liquid products is important to companies in the food, beverage and chemical manufacturing industries. These businesses use in-line filling machinery to ensure uniform product levels for packaging products in various types of containers.
UK based Mount Packaging Systems custom designs and manufactures a comprehensive line of filling systems ranging from semi-automatic, mobile filling machines to fully automatic turnkey systems. The company specialises in providing technical solutions for difficult filling applications for liquids and pastes including paints, chemicals, lubricating oils, adhesives and food products. To ensure accurate filling in final packaging, in-line filling machinery relies on systems that use precise measurement technology to prevent waste from overfilling and spillage, and to ensure volume and weight uniformity. Mount Packaging implemented Foxboro mass flowmeter technology to manage the wide range of viscosities, temperatures, chemical compatibilities and particulate sizes associated with materials processed by its worldwide customer base.
Conventional measurement methods
Over the years, Mount Packaging has implemented a variety of methods to help its customers achieve consistent, accurate measurement of the materials that its machines dispense. While customers have been largely satisfied with traditional measurement methods, the company was aware of certain limitations and identified measurement technology as an area for improvement. One of the conventional measurement methods used is volumetric piston filling, which uses a device external to the container to measure the volume of material being dispensed. While this type of filling is considered highly accurate, it has a limited turndown ratio of approximately 20:1 and poor repeatability at the bottom end of the range. In addition, trimming the fill size had to be done mechanically.
Weigh scales, another conventional measurement technology, are limited in a different way. They require trickle or ramping flow at the end of each fill, which is both time-consuming and causes spillage that can lead to erroneous readings. To overcome these limitations, Mount Packaging officials experimented with Coriolis flow measurement technology, which would measure dispensed volume based on flow rate rather than volume. However, conventional Coriolis meters had limitations as well. “We tried traditional Coriolis meters, but they did not deliver the repeatability we required,” said Kevin Beaumont, managing director at Mount Packaging. “While conventional Coriolis meters were very accurate with steady flow in longer batches, they lacked the ability to respond rapidly to flow changes during the course of short batches. When used with viscous fluids like paint, even small levels of gas in liquid (two-phase flow) skewed Coriolis readings.”
Foxboro Coriolis flowmeter successfully manages filling operations
Mount Packaging implemented the Foxboro CFT50 digital Coriolis mass flowmeter from Invensys. This technology is considered a ‘breakthrough’ for automated filling applications because it uses digital technology to keep flow tubes in constant motion so there is no loss of flow measurement during dynamic flow conditions.
Using this approach, the Foxboro CFT50 flowmeter re-tunes the drive frequency of the Coriolis flow tubes every half cycle which ensures consistency and reliability. Built-in algorithms also compensate digitally for inaccuracies resulting from two-phase flow. It is able to compensate for common industry problems associated with entrained gases, empty tubes or flash-prone fluids. The technology achieves high measurement accuracy, eliminates downtime and avoids workarounds to help keep profit flowing. Customers report the system provides exceptional performance in the world’s most challenging applications, including tanker and truck loading/unloading, centrifuge control, ethylene oxide processing, sanitary batching, pharmaceutical batching, and food/dairy/beverage measurement.
Research and testing pays off
Initially, Mount Packaging tested the Foxboro CFT50 flowmeter on a 40 mm flow tube with a nominal flow capacity of 6,8 kilograms/second. This resulted in the meter producing pulses that correlate with product weight. For example, three pulses per milliliter of flowing liquid are transmitted to a PLC which counts them and is programmed to actuate the shut-off valve when the target fill weight is achieved. Flowmeters are designed to measure flow of liquids by analysing changes in Coriolis force of the substance in which the Coriolis force arises from a mass moving within a rotating frame of reference. The rotation produces an angular, outward acceleration. Combining this with linear velocity defines the Coriolis force. A Coriolis meter’s two main components include an oscillating flow tube equipped with sensors and drivers, and an electronic transmitter that controls the oscillations, analyses the results and transmits the information.
Invensys collaborated with researchers at Oxford University in England to develop digital technology for accurate measurement of flow, even when the flow tube contains entrained air. The group developed the Foxboro CFT50 flowmeter which incorporates new signal processing techniques to provide useful measurements of both mass flow and density, and the operational aspects of keeping the Coriolis meter running stably in single-phase or two-phase flow conditions. One processing system controls the meter drive sequence to provide uninterrupted flow tube operation. The second system processes the measurement data from the Coriolis meter, which ensures precise fluid measurements. Coriolis meters provide direct measurement of mass flow, which is highly desirable in applications requiring precise measurement. This is particularly true for difficult-to-meter materials such as slurries and homogeneous fluids. In addition, the CFT50 reduces overall cost of ownership since the meter continues to operate uninterrupted, eliminating loss of production. Maintenance and operating costs also can be reduced since the flowmeter can be used in applications with a wide variety of fluids without re-calibration.
After a few trial runs, Mount Packaging was able to establish new flow profiles for the batch runs, which demonstrated considerably improved measurement potential. “Mount Packaging learned to trust the meter,” says Beaumont. “The company adjusted its equipment to improve performance and we are getting excellent repeatability with the Foxboro CFT50 Coriolis mass flowmeter. We can now prevent lost production, eliminate inaccurate pricing concerns and avoid excess downtime.”
For more information contact Jaco Markwat, Invensys Operations Management, +27 (0)11 607 8100, [email protected], www.iom.invensys.co.za
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